Probably because the King Air is the most popular corporate turboprop every built and Beechcraft has manufactured over 6,000 units since 1964, many third party companies have come up with modifications for most models. Most of the mods enhance performance, safety, comfort, utility or all of the forgoing. Although all the enhancements are available as after-­‐market ad-­‐ons to your King Air by third-­‐party manufacturers, many of these enhancements have been integrated into the newer models or are now installed by the factory at the time production.

Summarized below are the many modifications for each series and a brief explanation of each modification. Most of these modifications have been designed by Raisbeck Engineering, a company that has built a solid reputation since 1982 for enhancing King Air performance and utility.

Dual Aft Body Strakes -­‐ Two fins designed by Raisbeck Engineering that replace the the single fin on the lower aft section of the tail. The modification improves directional stability and pilot control, improves passenger ride quality, reduces drag and increases yaw-­‐damper inoperative altitudes. In most King Airs an inoperative yaw damper will reduce the upper altitude limit that you can fly, but not with the dual aft body strakes. The cost is around $20,000. ​​​​​​

High Float Landing Gear Doors - New main landing gear doors designed by Raisbeck engineering that cover the high flotation landing gear (larger gear for unimproved runways and short fields) which increase aerodynamics and result in restoring original climb and cruise performance lost with the high flotation gear option.

Crown Wing Lockers - Streamlined storage space designed by Raisbeck engineering installed aft of the engines which adds baggage storage space outside the cabin. Excellent for golf clubs, skis, and small surfboards. The cost for the Wing Lockers is around $58,000.

Ram Air Recovery - The Raisbeck-patented Ram Air Recovery System is a modification of the engine inlet and maximizes the air to the engine inlet so that your engine retains the same power with ice vanes deployed that you get now with the ice vanes stowed. Your aircraft retains speed and power as you climb through clouds or inclement weather. With ice vanes stowed, you experience increased power and speed, and you save fuel - all at lower engine temperatures. The cost for the Ram Air Recovery is around $42,000.

Enhanced Performance Leading Edges - Modification designed by Raisbeck Engineering to the inboard leading edge of a King Air 200 series wing that increases climb and cruise performance, reduces stall speeds, reduces wing structural fatigue and provides more efficient air conditioning. The cost is around $34,000.

Four Blade Props - There are various modifications that change out the original 3-blade props in the older models for the new 4-blade props. Some models reduce vibration, increase performance and increase the time between overhauls.

Raisbeck Swept Propellers - In 2013 Raisbeck Engineering of Seattle came out with swept blade turbofan propellers for the 200, B200 and B200GT improves take of distances by 1,090 feet, accelerate-go distances by 3,450 feet, reduces landing distances by 530 feet and lowers Vref speeds by nine knots. It cuts time to climb to 33,000 feet by 7 minutes (29 to 22 mintues) and increasing cruise speed at 33,000 feet in a stock King Air by 13 knots. The props are 3” longer than the stock 93” prop. Price is around $85,000 per set.

Speed Stacks - Aerodynamic exhausts pipes for 90 and 100 series King Airs designed by American Aviation which increase cruise speed and reduce engine exhaust residue on the airframe.

Frakes Stacks - Aftermarket exhaust stacks for all King Airs designed and manufactured by Frakes Aviation which significantly reduce soot accumulation on the engine nacelles.

Pitot Cowls - Modified cowlings designed by American Aviation for older 90 and 100 series King Airs that significantly increase cruise speed by 10 to 20 knots. Cowlings are similar to the cowlings on 90 series found in the C90B and newer 90 series models. Cost is around $52,000. We have seen direct evidence of an honest improvement in cruise speeds in a 1975 C90 from 220 knots to 240 knots.

Engine modifications:
Replacing the standard PT6A-21 engines with new PT6A-135A's increases true airspeed in the 90 series King Airs by 20 to 30 knots, depending on the model King Air 90. 90 Series with the the pitot cowls, C90A's and C90B's will cruise at around 270 knots, while older C90's and E90's will cruise at around 260 knots. There is also modification that replaces the PT6A-21 with a PT6A-35, which provides the identical performance of the PT6A-135’s.
Replacing the standard PT6A-42 and -41 engines with new PT6A-52 or -61 engines will increase true airspeed in the 200 series King Airs by 14 to 26 knots, depending on the model King Air 200. Frequently the modifications to 200 series are coupled with other Raisbeck modifications such as enhanced leading edges and ram air recovery to obtain even more speed. You can also install the Hartzell/Raisbeck 94" four-blade propellers prior to King Air B200 serial number BB-1509. After BB-1509 the Hartzell/Raisbeck 93" propellers were installed as standard by the factory during production.
Raisbeck refers to the installation of the ram air recovery system, enhanced leading edges, dual aft body strakes, new propellers, and crown wing lockers as the Raisbeck Epic Platinum package. For newer King Air B200's, post serial number BB-1509, the package is referred to as the Raisbeck Epic Gold package and it excludes the propellers because the Raisbeck/Hartzell 93" propellers became standard as part of the Beechcraft factory's standard equipment.